This invention relates to electrical ignitor plugs such as are commonly used in electric cigar lighters, combustion engines, and the like; more particularly it relates to the securing of the outer end of a spiral heating coil to the rim of a metal holder or container cup therefor.
In the past it has been a common procedure to outwardly offset the outer end of a spiral heating coil of a cigar lighter or other ignitor and then spot weld the end to the inner wall of a metal container cup. While such an arrangement has been considered satisfactory and has been practised for many years, it has inherent disadvantages and drawbacks. In order for the completed unit to perform satisfactorily throughout the useful life of the coil, the weld at the outer end must be sufficiently secure not to loosen under the action of heat and physical stresses; however, the welding operation should not have progressed to the extent where the resistance ribbon becomes weakened and loses its physical and electrical characteristics, causing burn-out or breakage to occur at a later time.
In order to obtain a product which is satisfactory in meeting the above conditions, it has been necessary to inspect carefully the welds that are made. For the ultimate in the quality of the product, a 100-per cent inspection is generally necessary. This inspection requires skilled personnel and represents an appreciable expense.
Moreover, during continuous volume production of igniting units of this type, frequent replacement of the welding electrode is necessary, involving down-time and the services of a tool setter. Replacement of electrodes as often as every 15 minutes is commonplace. The down-time, tool setter's labor, and cost of the electrodes further add to the expense of the igniting units.
Additionally, igniting units made in this manner present a raw and somewhat unfinished appearance when viewed head-on, the product appearing to be the result of temporary tooling rather than finished production tooling.
Other methods of securing the end of the heating element to the cup include staking and shearing, as in U.S. Pat. Nos. 3,012,127 and 3,573,428. These methods present the problem of orientation as well as resulting, as does the welding or brazing method, in small contact areas between the resistance ribbon and the cup.